FORTY YEARS OF QENECOLOGY
217
periodic treatment may be transmitted through many cell generations
without decay, and may, furthermore, be amplified and transmitted to
other plants by grafting. Indeed, having regard to this, what is remarkable is the efficiency of the mechanism which acts in the commonality of
cases to restore reproductive cells to a basal, undifferentiated and unconditioned state. That occasionally this restoration should be incomplete so that some proportion of a parental experience is transmitted to
progeny seems not at all unreasonable.
Durrant’s experiments illustrate one kind of transmission of acquired
characteristics; evidently it would be profitable now to reconsider the
possibility that some habitat-correlated variation may be due to direct
conditioning and subsequent transmission of the conditioned state to
progeny. It is interesting to note that there is no a priori reason to
expect conditioning invariably to produce adapted phenotypes, except
in so far as a principle like that of Crosby might be involved. This opens
the possibility of there being non-adaptive, habitat correlated variation.
However, there is as yet no direct evidence of such a phenomenon, and
in the succeeding discussion of the physiological aspects of genecological
differentiation it will not be taken into consideration.
111. PHYSIOLOGICAL ASPECTS OF
G ENECOLOGICAL DIFFERENTIATION
A. INTRODUCTION
The detection of genecological differentiation within a species
generally depends in the first instance upon the observation of habitatcorrelated variation in morphological features. As we have seen (p. 168)
it is presumed that if populations in one type of habitat are regularly
found to differ from those in another in any characteristics whatever,
those differences (or others unobserved genetically or developmentally
correlated with them) must have adaptive significance, because the only
plausible cause of the divergence, discounting the kind of conditioning
mentioned in the foregoing section, is the differential effect of selection
in the two environments.
This argument depends not in the least upon any physiological interpretation of the differences. Yet it is difficult to arrest genecological
investigation at the point where presumed adaptive differences have
merely been identified, for the question of their actual survival value in
the habitats concerned then obtrudes itself. An important matter to
clear up is the level at which answers to questions of this type would be
deemed acceptable. Consider the case of two “ecotypes” A and B, from
two habitats, a and b. In habitat a, A performs better than B as assessed
by some arbitrary measure such as dry matter accumulation, and in
217
periodic treatment may be transmitted through many cell generations
without decay, and may, furthermore, be amplified and transmitted to
other plants by grafting. Indeed, having regard to this, what is remarkable is the efficiency of the mechanism which acts in the commonality of
cases to restore reproductive cells to a basal, undifferentiated and unconditioned state. That occasionally this restoration should be incomplete so that some proportion of a parental experience is transmitted to
progeny seems not at all unreasonable.
Durrant’s experiments illustrate one kind of transmission of acquired
characteristics; evidently it would be profitable now to reconsider the
possibility that some habitat-correlated variation may be due to direct
conditioning and subsequent transmission of the conditioned state to
progeny. It is interesting to note that there is no a priori reason to
expect conditioning invariably to produce adapted phenotypes, except
in so far as a principle like that of Crosby might be involved. This opens
the possibility of there being non-adaptive, habitat correlated variation.
However, there is as yet no direct evidence of such a phenomenon, and
in the succeeding discussion of the physiological aspects of genecological
differentiation it will not be taken into consideration.
111. PHYSIOLOGICAL ASPECTS OF
G ENECOLOGICAL DIFFERENTIATION
A. INTRODUCTION
The detection of genecological differentiation within a species
generally depends in the first instance upon the observation of habitatcorrelated variation in morphological features. As we have seen (p. 168)
it is presumed that if populations in one type of habitat are regularly
found to differ from those in another in any characteristics whatever,
those differences (or others unobserved genetically or developmentally
correlated with them) must have adaptive significance, because the only
plausible cause of the divergence, discounting the kind of conditioning
mentioned in the foregoing section, is the differential effect of selection
in the two environments.
This argument depends not in the least upon any physiological interpretation of the differences. Yet it is difficult to arrest genecological
investigation at the point where presumed adaptive differences have
merely been identified, for the question of their actual survival value in
the habitats concerned then obtrudes itself. An important matter to
clear up is the level at which answers to questions of this type would be
deemed acceptable. Consider the case of two “ecotypes” A and B, from
two habitats, a and b. In habitat a, A performs better than B as assessed
by some arbitrary measure such as dry matter accumulation, and in